1. Field of the Invention
The present invention relates to a liquid crystal display device. In particular, one where the existence or non-existence, shape, etc. of the transfer column can be observed without forming a monitoring window. The present invention also relates to a method of manufacturing the liquid crystal display device.
2. Prior Arts
Hereafter, the conventional liquid crystal display devices will be described with reference to the Figures.
FIG. 1 is an aerial view showing the configuration of the conventional liquid crystal display device from the viewpoint of the display surface side, and FIG. 2 is an equivalent circuit diagram illustrating the structure outline of this type of liquid crystal display device.
As shown in FIG. 1, the active matrix-type liquid crystal display device, which uses Thin-Film Transistors (hereafter, TFTs) as switching elements, is composed of a TFTs substrate 100 and a color filter substrate 20. Wherein, the TFTs substrate 100 has TFTs and pixel electrodes 30 arranged in matrix form, whereas the color filter substrate 20 is made of a shielding film (namely a black matrix) 23, a coloring layer, and a common electrode. The above two substrates 100 and 20 face each other across a liquid crystal.
In FIG. 2, reference numeral 41 depicts gate lines or scanning lines driven by a gate bus line driver (not shown in the Figure), which is connected to the gate terminals 31. Reference numeral 42 depicts drain bus lines or signal lines driven by a drain bus driver (not shown in the Figure), which is connected to the drain terminals 32. Reference numeral 47 depicts TFTs, where their gates are connected to the gate bus line 41, and their drains are connected to the drain bus lines 12. Reference numeral 46 depicts pixel electrodes, which are connected to the respective TFTTs 47, and which are formed of a transparent conductive film such as ITO.
The area of a color filter substrate 20 is overlapped with a partial area of the TFTs array substrate 100, wherein the substrates 20 and 100 face each other across a liquid crystal, as is mentioned above.
Each accumulation capacitor element 45 and liquid crystal capacitor element 44, are connected parallel to each other. In addition, they are connected to their corresponding TFT 47 in series. Each accumulation capacitor element 45 is formed of a pixel electrode 46 and an accumulation capacitor electrode (not shown in the Figure), where an insulating film is sandwiched between these electrodes. Whereas, each liquid crystal capacitor element 44 is formed of a pixel electrode 46 and an electrode (not shown in the Figure) facing the electrode 16, which is located on the surface of the color filter substrate 20; wherein the liquid crystal is sandwiched between the above two electrodes. In result, the common voltage, which is input from the common voltage input terminals 33 and formed on the surface of the TFTs array substrate 100, is supplied from the transfer pads to the respective, facing electrodes via the transfer columns 27.
The structure and manufacturing method of the representative conventional TFTs array substrate will be described with reference to FIGS. 3 and 4.
FIG. 3 is an aerial view showing the structure of a pixel section, according to the first example of conventional TFTs array substrates, and FIG. 4 is a cross section of FIG. 3 cut along the line of A-A'.
In FIGS. 3 and 4, first of all, a gate electrode 1, a gate bus line 11 (see FIG. 3) and an accumulation capacitor electrode are formed on top of the glass substrate 101 by patterning the first metal film, made of a metal such as Cr or Al. In addition, in FIG. 3, a part of the gate bus line 11 also acts as an accumulation capacitor electrode. Afterwards, a gate insulating film 14, made of a material such as silicon oxide film or silicon nitride film; a channel layer 2, made of intrinsic semiconductor non-crystalline silicon (hereafter, [a-Si (I)]); and a contact layer 7, made of n-type semiconductor non-crystalline silicon (hereafter, [a-Si (n+)]), are successively formed. Next, the patterning process etches off part of the gate insulating film 14; wherein, the part corresponds to the regions (not shown in the Figures) where terminals used for interfacing with a driver IC are to be formed. Then, a through-hole (not shown in the Figures), which is used to electrically interface a first metal film comprising the gate electrode 1 with a second metal film (where a drain electrode 3, a source electrode 4, and a drain bus line 12 are to be formed from this second metal film later), is formed. Afterwards, in the same way as the gate electrode 1, the second metal film, made of a metal such as Cr or Al, is patterned, so as to form the drain electrode 3, the source electrode 4, and the drain bus line 12. A transparent conductive film consisted of a transparent conductive material such as ITO, is formed as a pixel electrode 6. Subsequently, the contact layer 7 is etched, so as to remove part of its area on top of the channel layer 2. Afterwards, by the formation of a passivation film 15, which is made of a material such as silicon nitride, the TFTs array substrate 100 is completed. It is noted that the passivation film 15 located on top of the pixel electrode 6 is removed, in order to prevent a drop in device transmittance, namely a drop in brightness of the display, which causes the absorption of light for the passivation film 15. That is to say, as shown in FIGS. 3 and 4, a passivation film aperture region is provided to cover almost the entire surface of the pixel electrode 6.
Next, the structure and manufacturing method of the transfer pad, which is formed on top of the first example of conventional TFTs array substrates, will be explained hereafter, with reference to the Figures.
FIG. 5 is an aerial view showing the configuration of the transfer pad formed on top of the first example of conventional TFTs array substrates, and FIG. 6 is a cross section of FIG. 5 cut along the line of A-A'. The manufacturing method and process described below, is the same as the TFTs array substrate described earlier with reference to FIGS. 3 and 4.
In FIGS. 5 and 6, first of all, a first metal film 301, which is made of a metal such as Cr or Al, is formed. It is then patterned into the shape of a transfer pad. Afterwards, a gate insulating film 14, made of a material such as silicon oxide or silicon nitride, is formed on top of the glass substrate 101. Then, a patterning process etches off a predetermined area of the gate insulating film 14 on top of the first metal film 301, so as to form the through hole 9, which is used to electrically interface the first metal film 301 with the second metal film 303. Next, the second metal film 303, made of a metal such as Cr or Al, is patterned into a fixed shape in the same way as the first metal film 301. Next, the transparent conductive film 306, made of a transparent conductive material such as ITO, is formed on top of the second metal film 303 mentioned above. Subsequently, through the formation of the passivation film 15, made of a material such as silicon nitride, the transfer pad is formed. At this point, the passivation film 15, located on the surface of the transparent conductive film 306, is removed to electrically connect the transfer pad and transfer column 24. Namely, as shown in FIGS. 5 and 6, the aperture region of the passivation film 15 is provided on top of the transparent conductive film 306. This transfer pad is connected to the common voltage input terminal 33 (see FIGS. 1 and 2), via one or both of the first or second metal films 301 and 303.
In the first example of conventional TFTs array substrates, previously described with reference to FIGS. 3 and 4, the drain bus line 12 and the pixel electrode 6 are both formed on top of the gate insulating film 14. That is to say, they are both formed on the same plane, and are adjacent to each other at a certain interval. Therefore, when a bad pattern results from the patterning process, the drain bus line 12 and the pixel electrode 6 are apt to short. When there is a short in the drain bus line 12 and the pixel electrode 6, the charge and discharge in the pixel electrode 6 cannot be controlled by turning on or off its corresponding TFT, and this pixel is registered as a point defect.
In result a TFTs structure, which reduces the potential for the drain bus line 12 and the pixel electrode 6 to short, is proposed.
This TFT will be explained hereafter, with reference to the Figures, as the second example of conventional TFTs array substrates.
FIG. 7 is a plan illustrating the structure of a pixel section of the second example of conventional TFTs array substrates, whereas FIG. 8 is a cross section of FIG. 7 cut along the line A-A'.
Hereafter, the manufacturing method of the TFTs array substrate will be described with reference to the Figures.
In FIGS. 7 and 8, first of all, a gate electrode 1, a gate bus line 11 and an accumulation capacitor electrode are formed on the surface of the glass substrate 101 by patterning a first metal film, made of a metal such as Cr or Al. In addition, in FIG. 7 and as in FIG. 3, a part of the gate bus line 11 also acts as an accumulation capacitor electrode. Afterwards, a gate insulating film 14, made of a material such as silicon oxide or silicon nitride, a channel layer 2, made of a-Si (I), and a contact layer 7, made of a-Si (n+) are successively formed. Next, the gate insulating film 14 is patterned, so as to etch off part of it, wherein, the part corresponds to the areas of prospective terminals that will be formed later in order to interface with a driver IC. Through the patterning process, a through-hole (not shown in the Figures), which is used for electrically connecting the first metal film comprising a gate electrode 1, to the second metal film, is formed. Afterwards, in the same way as the gate electrode 1, the second metal film made of a metal such as Cr or Al is patterned, so as to form a drain electrode 3, a source electrode 4 and a drain bus line 12. Subsequently, a contact layer 7 on top of the channel layer is partially etched off. On top of this, after the formation of a passivation film 15, a through-hole 10 is then formed, so as to electrically connect a to-be-formed pixel electrode 6 to the source electrode 4, made of the second metal film. Thereafter, the pixel electrode 6 is formed on top of the resulting surface, so as to complete forming TFTs array substrate 100. Also, the necessary number of patterning steps for this structure described is the same as for the structure described with reference to FIGS. 3 and 4.
In the structure of one pixel of the second example of conventional TFTs, the drain bus line 12 is formed on top of the gate insulating film 14, and on the other hand, the pixel electrode 6 is formed on top of the passivation film 15. The passivation film 15 or insulating film, formed between the drain bus line 12 and the pixel electrode 6, prevents an occurrence of a short circuit between them, even if they are imperfectly patterned. Thus, bad point defects are reduced.
Next, the structure of the transfer pad, which is formed on the second example of conventional TFTs array substrates, will be described hereafter, with reference to the Figures.
FIG. 9 is a plan of a transfer pad, which is formed on the first example of conventional TFTs array substrates, whereas FIG. 10 is a cross section of FIG. 9 cut along the line A-A'. FIG. 11 is a plan of a transfer pad, which is formed on the second example of conventional TFTs array substrates, whereas FIG. 12 is a cross section of FIG. 11 cut along the line A-A'. The manufacturing method and process described below, is the same as for the TFTs array substrate previously described with reference to FIGS. 7 and 8.
To start, the first example of the structure of a transfer pad will be described.
As shown in FIGS. 9 and 10, the first metal film, made of a metal such as Cr or Al, is formed on top of the glass substrate 101. It is then patterned into the fixed shape of a transfer pad. The gate insulating film 14 made of a material such as silicon oxide or silicon nitride is formed next. Subsequently, the passivation film 15, made of a material such as silicon nitride, is formed. Then, in order to electrically connect the first metal film 301 to the transparent conductive film 306, both the gate insulating film 14 and the passivation film 15, located on the first metal film 301, are partially etched off, so as to form the through-hole 10 (see FIG. 11). Next, the transparent conductive film 306, made of a transparent conductive material such as ITO, is formed on top of the aforementioned first metal film 301. As a result, the fabrication of a transfer pad is completed. This transfer pad is connected to the common voltage input terminal 33, via the first metal film 301.
Next, the second example of the structure of a transfer pad will be described.
As shown in FIGS. 11 and 12, a gate insulating film 14, made of a material such as silicon oxide and silicon nitride, is formed on top of a glass substrate 101. A second metal film 303, made of a metal such as Cr or Al, is formed on the resulting surface. It is then patterned into the fixed shape of a transfer pad, and then a passivation film 15, made of a material such as silicon nitride, is formed. Here at the same time, in order to electrically connect the second metal film 303 to a to-be-formed transparent conductive film 306, the passivation film 15, located on top of the second metal film 303, is partially etched off. Next, the transparent conductive film 306, made of a transparent conductive material such as ITO, is formed on top of the aforementioned second metal film 303. In result, the fabrication of the transfer pad is completed. This transfer pad is connected to the common voltage input terminal 33, via the second metal film 303.
Next, the manufacturing method of the liquid crystal display device, which uses the previously described first and second examples of conventional TFTs array substrates, will be described with reference to the Figures.
In FIG. 12, the color filter substrate 20 is composed of the glass substrate 21; the black matrix 23, which is made of a metal such as Cr or CrOx, and black resin, on the surface of the substrate 21; and a coloring layer (not shown in the Figure). Wherein, in order to confirm the existence or non-existence and shape of the transfer column, a part of the black matrix 23 is removed, so as to form a transfer column-monitoring window (see FIG. 1). A facing electrode 22, made of a transparent conductive film material such as ITO, is formed on the resulting surface. In result, the fabrication of a color filter substrate 20 is completed.
An orientation processing film (not shown in the Figure) is formed on each of the surfaces of the TFTs array substrate 100 and color filter substrate 20. Next, a seal (not shown in the Figure) made of an adhesive, is formed along the rim of the outer area of the color filter substrate 20. A transfer column 24, made of a material such as silver paste, is then formed in the four corners of the color filter substrate 20. In addition, the transfer column 24 is formed in order for the transfer pad, which is formed on top of the TFTs array substrate, and the facing electrode 22, formed on the surface of the color filter substrate, to be electrically connected to each other. Subsequently, the two substrates mentioned above are adhered at a fixed distance apart. Liquid crystal (not shown in the Figure) is then injected in between them, and is sealed shut. In result, the liquid crystal display device is completed.
Thereafter, a driving circuit, a case (not shown in the Figure), etc, are added to the polarizing plates 25 and 102 of the liquid crystal display device. In this case, the display is viewed from the glass side of the color filter substrate 20.
As mentioned above, in order to confirm the existence or non-existence and shape of the transfer column 24, a part of the black matrix 23 is removed, so as to form the transfer column-monitoring window 26. In result, the quality resulting from fabricating the transfer column 24 can be easily observed, even after the fabrication of the liquid crystal display device.
Nowadays, in order to control the drop in the image display quality, resulting from reflection off the surface of the liquid crystal display, low reflectance of the black matrix, which is made of CrOx and black resin, and such technology as low reflection processing of the polarizing plate 25, are adopted. In this case, there is a problem of dropping the quality of appearance of the liquid crystal display surface. That is to say, a problem in which the surface of the transfer column 24 can be clearly seen out of the transfer column-monitoring window, which is formed on the black matrix 23, from the viewpoint of the glass side of the display, namely the color filter substrate 20, as a displayed image is also seen at the same time. This emanates from the fact that the transfer column 24 made of material such as silver paste, which compared to the black matrix 23 and polarizing plate 25, has a relatively high reflection factor.
Furthermore, as a patent example concerning the structure of the transfer pad, the Japanese Patent Applications Laid-open Nos. Hei-8-327995 and Hei-7-159795 are open to the public.
The structure of the transfer pad presented in the Japanese Patent Application Laid-open No. Hei-8-327995) follows the structure mentioned above, except that a transfer column-monitoring window is not formed on the black matrix. Therefore, since the transfer column is not visible from the display side of the liquid crystal display panel, there is the problem of not being able to confirm the existence or non-existence and shape of the transfer column after having fabricated the liquid crystal display device.
Even though the techniques for decreasing poorly-formed seals and transfer columns are proposed in the Japanese Patent Application Laid-open No. Hei-7-159795, by having a guiding ditch formed in the region where the seals and transfer columns are formed, it does not have any relevance to the problems that are to be solved with the present invention.